Pushover Analysis as per EC8:2004

midas Gen tutorials

Pushover Analysis of RC structure as per EC8:2004

DL

Program Version

Gen 2010

Program License

Registered, Trial

Revision Date

SD

NC

2010.07.14 MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Overview

Pushover analysis is one of the performance-based design

Pushover Analysis Procedure The pushover analysis procedure is as follows:

methods, recently attracting practicing structural engineers engaged in the field of seismic design. The objective of a

 Modeling & Design

performance-based design is achieved after the user and the

- Details of Building

designer collectively select a target performance for the

- Perform analysis

structure in question. The engineer carries out the conventional

- Check assigned rebar data

design and subsequently performs a pushover (elasto-plastic)

analysis to evaluate if the selected performance objective has been met. In midas Gen, pushover analysis as per EN1998:2004 is provided. This tutorial explains the method and procedure for pushover analysis of 2-dimensional RC structural as per EN1998:2004. For this reason, the procedure for modeling and analysis were not explained in detail. For the users who are not familiar with the basic functions for modeling and analysis, it is recommended to review “Application 1” tutorial before

 Pushover Analysis

- Pushover Global Control - Pushover Load Cases - Define Hinge Properties - Assign Hinge Properties - Perform Pushover Analysis - Pushover Curve - Pushover Hinge Status Results - Safety Verification Table

following this tutorial.

2

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Details of the example structure G1

LB1

G1 C1

15@3,000 = 45,000

C1

unit : mm 4000

9000

1200

4000

9000

27200

Figure 1. Two-dimensional building model

Figure 2. Cross section

 Column section

3

 Beam section

Designation

Story

Section Number

Column Dimension

C1

12~15F 8~11F 4~7F 1~3F

104 103 102 101

600 x 600 700 x 700 800 x 800 900 x 900

Designation

Section Number

Section Dimension

G1

21

350 x 650

LBl

31

200 x 400

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials  Applied Design Code •Eurocode  Materials (Eurocode4:2004) •Column: C30/37 •Beam: C25/30 •Wall: C30/37

 Applied Loads Gravity loads •unit: kN/m2 •Use : Residential Static Wind Loads •Applied code: Eurocode1:2005 •Terrain Category : II • Fundamental Basic Wind Velocity (Vb,o) : 26m/s Static Seismic Loads •Applied code: Eurocode8:2004 •Ground Type: B •Design Ground Acceleration: 0.08g •Behavior Factor (q): 1.5 •Lower Bound Factor (b): 0.2 •Importance Factor (I) : 1 4

Unit Load Cases Load

Static Load Cases

Name

Details

1

DL

Dead Load

2

LL

Live Load

3

WX

Wind Load (X-direction in the global coordinates)

4

XY

Wind Load (Y-direction in the global coordinates)

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 1. Open the model file and perform analysis 1. Open “Pushover_2D RC structure.mgb” 2. Click

icon to perform analysis.

Pushover analysis is carried out in the post-processing mode after completing elastic analysis.

2

5

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials 1

4

Step 2: Check assigned rebar data 1. 2. 3. 4. 5. 6.

Design > Concrete Design Parameter > Modify Beam Rebar Data Check on the section ID 21. Check rebar data for Beam. Design > Concrete Design Parameter > Modify Column Rebar Data Check on the section ID 101. Check rebar data for column.

2

5

In order to calculate the yield strength for each member in pushover analysis, rebar must be assigned.

6

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 3: Check Concrete Design Code

1. 2. 3.

7

Design > Concrete Design Parameter > Design Code Specify the code as „Eurocode2:04‟. Check [OK] button.

Design Code specified in the Concrete Design Code dialog is applied to calculate the capacity of members in pushover analysis.

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 4: Pushover Global Control 1. 2. 3. 4. 5.

Design > Pushover analysis > Pushover Global Control Select DL in the combo box and click [Add] button. Select LL in the combo box and enter the Scale Factor as 0.4. Click [Add] button. Click [OK] button.

2

3 2

4

5

8

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 4: Pushover Global Control

„Reference Design code (Eurocode 8:2004)‟ option is displayed when the design code (in the main menu, Design > Concrete Design Parameter or Steel Design Parameter > Design code) is specified as Eurocode and Design code in preferences (in the main menu, Tools > Preferences…) is specified as Eurocode.

Tools -> Preferences… -> Select Design in the General

Scale Factor for Ultimate Rotation

1) Wall : In calculating the total chord rotation capacity at ultimate , θu, for wall , the value is divided by 1.6 as per EN1998-3:2004 A.3.1.1. 2) Cold-worked brittle steel : If cold-worked brittle steel is used the total chord rotation capacity is divided by 1.6 as per EN1998-3:2004 A.3.1.1. 3) Without Detailing for earthquake resistance : In members without detailing for earthquake resistance the total chord rotation capacity is multiplied by 0.85 as per EN1998-3:2004 . 4) Smooth longitudinal bars : in members with smooth (plain) longitudinal bars without lapping in the vicinity of the end region where yielding is expected, the total chord rotation capacity may be multiplied by 0.575 as per EN1998-3:2004.

9

MIDAS Information Technology Co., Ltd.

midas Gen tutorials

Pushover Analysis as per EC8:2004

Step 4: Pushover Global Control

Secondary Seismic Elements In order to calculate the total chord rotation capacity at ultimate, θu, the factor „γel’ is used. Since γel is differently applied for primary and secondary seismic element (γel = 1.5 for primary seismic elements, γel = 1.0 for secondary seismic elements As per EN1998-3:2004 A.3.1.1), the user can define Secondary Seismic Elements group. If Secondary Seismic Elements are not defined, all the elements are considered as Primary Seismic Elements. In this tutorial, Secondary Seismic Elements are not defined since pushover hinge properties are assigned to primary elements only.

10

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 4: Pushover Load Case 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

2

Design > Pushover analysis > Pushover Load Cases Click [Add] button. Enter the pushover load case name as „PL‟. Enter the Increment Steps as „20‟. Check on „Use Initial Load‟ option. Check on „Consider P-Delta Effect‟ option. Select „Displacement Control‟ in the Increment Method. Select „Mater Node‟ option. Click the entry field and click the node no. 93 with the mouse in the model view. Enter the Max. Displacement as 0.12m. Uncheck the Limit Inter-Story Deformation Angle in the Analysis Stopping Condition Specify the Load Case as „EX‟ in the combo box and click [Add] button. 9 Click [OK] button.

3 4

5

6 7

8 10 11

12 12

13

11

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

2

Step 5: Define Pushover Hinge Properties – Moment Hinge

1. 2. 3. 4. 5.

Design > Pushover analysis > Define Pushover Hinge Properties Click [Add] button. Enter the pushover hinge properties name as „Beam‟. Check on „Fz‟ & „My‟ component. Click [Apply] button. 3

In order to check or modify the hinge properties, click [Properties…] button of the desired component.

4



5

12

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 6: Define Pushover Hinge Properties – PMM (Axial-Moment interaction) Hinge for Column

1. 2. 3. 4.

Enter the pushover hinge properties name as „Column‟. Select „P-M-M in Status Determination‟ option for Interaction Type. Check on „Fz‟ & „My‟ component. Click [Apply] button.

Coupled axial force-biaxial moment behavior is reflected by calculating the flexural yield strength of a hinge considering the effect of axial force.

1

2

3  4

13

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 7: Define Pushover Hinge Properties – PMM (Axial-Moment interaction) Hinge for Wall

1. 2. 3. 4. 5. 6.

Enter the pushover hinge properties name as „Wall‟. Select the Element Type as „Wall(CRB)‟. Select the Interaction Type as „P-M-M in Status Determination‟. Check on „Fz‟ & „My‟ component. Click [Apply] button. Click [Close] button. 1 2

3 6

4

5

14

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials Pushover Hinge Properties Yield strength of RC structures M={As2*fsc*(d-d2)}+M’ Where, As2= area of compression steel M’=K’bd2fck fsc=700(xu-d2)/xu ≤ fyd d2=effective depth to compression steel xu=(δ-0.4)d fyd=design yield strength of reinforcement

Flexural Hinge

Shear strength of reinforcement, VRd,S is the smaller value of:

Eurocode2:2004, Equation(6.8) and (6.9)

Shear strength of concrete, VRd,C is given by: Shear Hinge Eurocode2:2004, Equation(6.2a) and (6.2b)

Therefore, Shear strength, VRd is FY = max (VRd,s ; VRd,c) Where, αcw=1.0 αcc =1.0

fcd=αcc fck/γC γC=1.0

RC structures (Eurocode8-3:2004, Annex A.3.1) DY Eurocode8-3:2004, Equation(A.10b)

Flexural Hinge DU

Eurocode8-3:2004, Equation(A.1) 15

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 8: Assign Pushover Hinge Properties for Beams 1. 2. 3. 4. 5.

Select Girder members (Section ID 21:G1) from the Tree Menu. Design > Pushover analysis > Assign Pushover Hinge Properties Select Hinge Properties Type as „Beam‟ in the combo box. Click [Apply] button. Click [Close] button.

1

Right-click

3 4

16

5

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 9: Assign Pushover Hinge Properties for Columns 1. 2.

Select column members from the Tree Menu. Drag and drop the „Column’ hinge property from the Tree Menu to the Model Window .

Pushover hinge properties can be simply assigned to the selected elements by Drag & Drop.

1 Right-click

2

17

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 10: Assign Pushover Hinge Properties for Walls 1. 2.

Select column members from the Tree Menu. Drag and drop the „Wall‟ hinge property from the Tree Menu to the Model Window .

Pushover hinge properties can be simply assigned to the selected elements by Drag & Drop.

1 Right-click

2

18

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 11: Perform pushover analysis 1. 2. 3.

Click „Task Pane‟. Click „▼‟ icon and select „Analysis‟. Click „Perform Pushover Analysis’.

Task Pane displays work procedure for advanced

analysis

functions

and

description on input items so as to enable the user to work more easily. 2

midas program provides 4 types of advanced analysis features - Pushover Analysis, 3

Nonlinear

Time

History

Analysis, Time History Analysis and Material Nonlinear Analysis. In addition, Task Pane data can be saved in html format in the User Folder, so that the user can directly write or add the required input items for analysis.

1

19

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 12: Pushover Curve Click „Pushover Curve‟ in the Task Pane. Select „For Target Displacement (EC2/Masonry)‟. Enter the Ref. Peak Ground Acc. (Ag) as „0.15‟. Click [Draw] button.

1. 2. 3. 4.

2

1

3

4

For the detailed formula of the Target Displacement, refer to „ANNEX B DETERMINATION OF THE TARGET DISPLACEMENT FOR NONLINEAR STATIC (PUSHOVER) ANALYSIS, EN 1998-1:2004‟. The target displacement, which is obtained from the above, corresponds to the seismic demand of the Limit State of Significant Damage (SD). Target displacement of the Limit State of Near Collapse (NC) is taken equal to that of SD multiplied by 1.5. Target displacement of the Limit State of Damage Limitation (DL) is taken equal to that of SD divided by 2.5.

20

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 13: Hinge Status Results Click „Hinge Status Results‟ in the Task Pane. Select „Status of Yielding (EC8:2004)‟. Select the Components as „Ry‟. Check on „Legend‟ and „Deform‟. Specify the desire step in the combo box.

1. 2. 3. 4. 5.

5 Clicking and scrolling

Clicking on the graph

The user can also check hinge status results for each step by clicking on the step box and scroll or clicking on the pushover graph which is displayed in the black background.

2

3 1 4

21

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Step 13: Safety Verification Table 1. 2. 3. 4. 5. 6.

Click „Safety Verification Table‟ in the Task Pane. Select „Show All Elements’. Click [OK] button. Select „Significant Damage (SD)‟. Check on „My‟ and „Fz‟. Click [OK] button.

2 3

4 Safety Verification Table displays the comparison results between the demand and capacities of the elements as per EN1998-3:2004 Table 4.3. Safety verification shall be conducted of both ductile and brittle elements respectively. For ductile elements, 5

verification will be conducted in terms of deformation using mean values of properties divided by CF. For brittle elements, verification shall be conducted in terms of strength

6

22

using mean values of properties divided by CF and by partial factor.

MIDAS Information Technology Co., Ltd.

Pushover Analysis as per EC8:2004

midas Gen tutorials

Capacity of RC structures for assessment in the Safety Verification Table (Eurocode8-3:2004, Annex A.3.1)

*For ductile elements, mean values of properties divided by CF are used. For brittle members, mean values of properties divided by CF and by partial factor. 23

MIDAS Information Technology Co., Ltd.